Deaths as a result of hot weather are to soar over the next four decades as a result of climate change, researchers have predicted.

The number of annual death s in the UK that occur as a result of the heat will rise by 257% by 2050, they said.

Elderly people are most at risk, according to the new study.

While the number of excess deaths seen in the summer months will rise, those recorded in winter will actually decrease, they said.

Researchers wanted to try to determine the effect that climate change will have on temperature-related deaths in the coming decades.

Their study, published in the Journal of Epidemiology and Community Health, examined fluctuations in weather patterns and death rates between 1993 and 2006 to characterise the associations between temperature and mortality.

The researchers, from Public Health England (PHE) and the London School of Hygiene and Tropical Medicine, then looked at projected population and climate increases so they could estimate temperature-related deaths for the UK in coming decades.

Researchers noted a 2.1% increase in the number of deaths for every 1C rise in the mercury and a 2% increase in mortality for every 1C drop in temperature.

The number of hot weather days is projected to rise steeply, tripling by 2080, they said. Meanwhile the number of cold days is expected to fall, though at a less dramatic pace.

At present there are around 41,000 winter-related deaths and 2,000 excess summer deaths.

The authors predicted that without adaptation , the number of heat-related deaths will increase by 66% in the 2020s, 257% by the 2050s and 535% by the 2080s.

Cold weather-related deaths will increase by 3% in the 2020s, then decrease by 2% in the 2050s and by 12% in the 2080s, they added.

This means by 2080 there will be around 12,500 heat-related deaths and 36,500 cold-related deaths.

The authors said that the burden of extreme weather remains such higher in those over the age of 75, particularly in the over-85s.

At present there are regional variations in excess temperature -related deaths and these are likely to persist, they added.

The south and the Midlands are the regions most vulnerable to heat while Wales, the north west, the east of England and the south are most vulnerable to the cold.

"The most direct way in which climate change is expected to affect public health relates to changes in mortality rates associated with ambient temperature," they wrote.

"In the UK, thousands of preventable deaths occur naturally from cold weather and a smaller burden is also associated with hot weather.

"Future changes in climate are likely to lead not only to an increase in heat-related deaths in the UK, but also a proportionally smaller decrease in cold-related deaths."

They added: "Our results indicate that health protection from hot weather will become increasingly necessary this century, and measures to reduce cold impacts will also remain important.

"Air conditioning is likely to become more widely used in the UK, which will reduce heat vulnerability. However, the distribution of cooling systems may reflect socio-economic inequalities unless they are heavily subsidised, and rising fuel costs may exacerbate this."

Dr Sotiris Vardoulakis, head of the PHE's air pollution and climate change group and co-author of the paper, said: " During periods of warmer weather higher temperatures can lead to greater-than-usual stress on the body caused by heat and higher levels of air pollution, which can aggravate the symptoms of those with chronic conditions, such as cardiovascular and respiratory conditions.

"This paper has again pointed to the anticipated growth of the UK's elderly population, broadly the most at-risk group from the effects of heat, and again states that because the UK elderly population will grow over the coming years, it will be even more important to plan how the country will cope with forthcoming temperature rises."

David Spiegelhalter, professor of the public understanding of risk at the University of Cambridge, said: "It seems clear from this analysis that the reduction in cold-related deaths per 100,000 people in each age group easily outweighs the projected increase in the heat-related death rate.

"So, were the population make-up to stay the same into the 2080s, temperature-related deaths would actually fall.

"Therefore it would be more accurate to say that increased number of future temperature-related deaths was wholly driven by projected population growth and ageing."